Handy solution to *joltup/rn-fetch-blob* iOS parallel download broken problem

app.js

var DownloadManagerIOS = NativeModules.DownloadManager;


DownloadManagerIOS.downloadList(imageLinkListForIOS, (el) => {
       // el is list of path
});

DownloadManager.h

//
//  DownloadManager.h
//
//  Created by Mohammad Julfikar on 22/05/2019.
//  Copyright © 2019 Facebook. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "RCTBridgeModule.h"

NS_ASSUME_NONNULL_BEGIN

@interface DownloadManager : NSObject<RCTBridgeModule>

@end

NS_ASSUME_NONNULL_END

DownloadManager.m

//
//  DownloadManager.m
//  ESv2
//
//  Created by Mohammad Julfikar on 22/05/2019.
//  Copyright © 2019 Facebook. All rights reserved.
//

#import "DownloadManager.h"

@implementation DownloadManager

RCT_EXPORT_MODULE();
RCT_EXPORT_METHOD(downloadList:(NSArray*)data savedPath:(RCTResponseSenderBlock)callback){
  
  NSMutableArray *finalList = [[NSMutableArray alloc]init];
  
  size_t size = data.count;
  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
  NSString *documentsPath = [paths objectAtIndex:0];
  NSFileManager *fileManager   = [NSFileManager defaultManager];
  
  documentsPath = [NSString stringWithFormat:@"%@/Downloads/Images",documentsPath];
  
  NSError *error = nil;
  if(![fileManager createDirectoryAtPath:documentsPath withIntermediateDirectories:YES attributes:nil error:&error]) {
    NSLog(@"Failed to create directory \"%@\". Error: %@", documentsPath, error);
  }
  
  NSOperationQueue *queue = [[NSOperationQueue alloc] init];
  queue.maxConcurrentOperationCount = 4;
  
  NSBlockOperation *completionOperation = [NSBlockOperation blockOperationWithBlock:^{
    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
        callback(@[finalList]);
    }];
  }];

  for (size_t i = 0; i < size; i++){
    NSString* trimmedUrlString = [data[i] stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
    NSURL *url = [NSURL URLWithString:trimmedUrlString];
    
    NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
      NSData *data = [NSData dataWithContentsOfURL:url];
      NSString *filename = [documentsPath stringByAppendingPathComponent:[url lastPathComponent]];
      if (![[NSFileManager defaultManager] fileExistsAtPath:filename] && data != nil)
      {
        if([data writeToFile:filename atomically:YES])
        {
          //NSLog(@"Saved");
          [finalList addObject:filename];
        }
        else
        {
          NSLog(@"Failed to download");
        }
      }
      
    }];
    [completionOperation addDependency:operation];
  }
  [queue addOperations:completionOperation.dependencies waitUntilFinished:NO];
  [queue addOperation:completionOperation];
}

@end